In the stabilization of conventional flexible polyurethane foam a careful balance of properties must be achieved. Two of the more important surfactant-dependent properties which must be balanced are height of rise and foam porosity. For good heights of rise the foam bubbles need to maintain their integrity (remain closed) to achieve the full potential of the expanding gases, i.e. low density, with a minimum density gradient from the top to bottom of the foam. The types of foam used for furniture cushions and bedding must also ultimately have a large fraction of open cells.
An excessive number of closed cells will cause the foam to shrink and distort as the gases within the closed cells start to cool. Also, if too many cells are closed or partially closed the foam will lack resiliency, that is, after being subjected to distortion the foam will not return rapidly to its original configuration. Thus, the ideal surfactant for polyurethane foam would allow essentially all of the bubbles to stay intact until the foam approached its maximum rise, but at that point it would be desirable for a high percentage of cell walls to open without damaging the skeletal network of the foam. It is also important that there not be densification at the bottom of the foam.
Within the commercially useful concentration range of surfactants, one has historically found an inverse relationship between height of rise and foam porosity. Thus, as air flow (breathability) increases there is generally a predictable loss in height of rise (i.e. increased density).
In some commercially used polyurethane foam formulations it becomes necessary to increase the surfactant concentration to achieve finer or more uniform cells in the foam. With most commercial surfactants, increasing the surfactant concentration causes an undesirable decrease in foam porosity.
The use of mixed polyether reactants to form flexible polyurethane foam surfactants were first described by R. Gerd in U.S. Pat. No. 3,637,541 in 1972.
This patent appears to cover both hydrolyzable and non-hydrolyzable types of silicone surfactants, i.e., those having SiOC and SiC linkages respectively, to polyethers. The first of the two polyethers employed had a m.w. range of 1600-4000 and contained 20-100% ethylene oxide units, and the second had a m.w. range of 400-1200 and contained 65-100% ethylene oxide.
The merits of using a blend of polyethers of high and low molecular weight (all having essentially the same ethylene oxide content) to form "hydrolyzable" silicone surfactants for flexible polyurethane foam was recognized in a UCC patent to Litteral, Mullins and Lee, U.S. Pat. No. 3,980,688 in 1977. These surfactant structures produced foams having a better combination of air flow and height of rise than could be achieved with siloxane-polyether copolymers derived from a single polyether.
No suggestion was made in either of these patents to react polyethers separately with silicones to make high efficiency cell openers which could be used as additives for primary surfactants.
Several examples can be found in the literature of silicone surfactants which have been improved by addition of organic or other surfactants. Most of these were employed in applications other than conventional flexible polyurethane foam, such as rigid polyurethane foam, high resilience polyurethane foam, and polyester foam. A polyester foam surfactant composition which was a blend of a conventional polyester foam surfactant with an organic sodium sulfonate was taught in U.S. Pat. No. 3,594,334, issued in 1971. Subsequently a sulfonated castor oil was proposed as a co-surfactant for polyester foam in German patent 2,615,804, issued in 1977. Blends of cyanoalkyl-containing silicones and more conventional polyether-silicone surfactants have been shown to reduce the flammability of polyurethane foam. See U.S. Pat. No 3,935,123, issued in 1976. Improved surfactant compositions for rigid foam have been obtained using a combination of an organic surfactant and a standard silicone surfactant. See U.S. Pat. No. 4,751,251, issued in 1988.
A recent European patent application by Dow Corning Corporation, EP 0 354 511 Al, teaches that mixtures of conventional silicone surfactants with an organic surfactant such as Pluronic P-84 produce foams having improved air flows. In an example, an improvement in air flow from 7 ft.sup.3 /min to 8 ft.sup.3 /min was seen when a 50/50 mixture was used.
German patent 3928867 Cl of Kollmeier et al. discloses amino-containing silcone-polyether copolymers as cell openers for certain polyurethane foams.
There are also examples in the literature of high resilience urethane foams stabilized with blends of surfactants. See, for example, the patent application by Baskent and Prokai described in CA96(22):182547w. This reference discloses using a conventional surfactant for high resilience foam and minor amounts of a conventional flex foam surfactant to improve foam stability.
It would be desirable to be able to increase urethane foam porosity by &gt;20% without losing more than a few percent in height of rise. It would be very desirable to be able to increase foam porosity by 50% or more with essentially no loss in height of rise. This need is answered by the "cell opener" materials of the present invention.